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Figure 1. The nesting crawl and nest location of a green turtle on Réunion Island. Lower panel shows amount of sand lost after a tropical cyclone passed the island.

On 27 January 2007, four tracks and one nest of green turtle were sighted on Cap Lahoussaye beach. The beach is narrow, and the female laid against a retaining wall next to a road running along the beach (Fig. 1). On 3 March 2007, a hurricane was forecast to pass near Réunion Island and cause a heavy swell that would have threatened the nest. An administrative authorization was given to translocate a part of the eggs to the artificial beach of the Kelonia, the marine turtle observatory. From the nest, 65 eggs were translocated and 30 eggs were left in the original location as a control. Egg incubation had reached 35 days at the time of relocation, hence it was important to maintain the axial orientation of each egg to avoid killing the embryos (Limpus et al 1979). To facilitate this, a cross was drawn on the top of each egg with a pencil before it was removed carefully from the nest. To protect the eggs from temperature shock during the transport, they were deposited on a sand bed, and then covered with a piece of linen and sand. In Kelonia, a 60 cm deep and cylindrical artificial nest was excavated, into which the eggs were placed delicately and then covered by the sand coming from the original beach. The weather degraded through the operation as the cyclone approached the coast. By the time the excavation was completed, rain began to fall.

Table 1. Monitoring of green turtle (Chelonia mydas) translocated nest coming from Cap Lahoussaye beach (nest 1), and in situ nests from one Saint Leu beach (nest 2 to 6), Réunion Island. Nests 2 to 6 were laid by the same female.

The 30 eggs left in the original nest were washed away by the hurricane-induced waves. From the translocated eggs, 40 hatchlings emerged 20 March 2007 (Table 1), and were released on the adjacent beach where nesting activity has regularly occurred since 2004. Post-emergence nest exhumation showed 9 undeveloped eggs (no obvious embryo) and 16 eggs with larger dead embryos at different development stages (Table 1). These eggs were located at the periphery of the nest.

Between the 01 June and 08 August 2007, 13 tracks were recorded on one beach of St Leu. The monitoring put in place by Kelonia’s staff suggested that the tracks were left by the same female, and she laid five nests during this period. Each nest were located by the staff and left in situ, with no sign to indicate their position to beachgoers. Because of the exceptional nature of nesting activities on the island, there was a concern that any sign would attract too much curiosity and have a negative impact on the eggs and hatchlings. Regular monitoring allowed the staff to assist with full or partial hatchlings emergence events. 40 hatchings from translocated nest and 216 hatchlings from 5 nests were measured and released to the ocean (Table 2).

Table 2. Mass and straight carapace length (SCL) recorded from hatchlings green turtle nests on the west coast of Réunion Island. n = number of hatchlings measured. Means given ±SD.

Delayed translocation may not be the main factor influencing on hatchling success as it was shown in Abella (2007). The survival rate observed for the translocated eggs (61.5%) is close to the mean survival rate (57.0% (range: 28.6 - 88.9%) observed for the other 5 in situ nests laid in 2007 in St Leu. One of these nests had a low survival rate (28.6%), likely due to its location under a tree on the beach that is also used by beachgoers during the day; inadvertent trampling was likely the main contributor to the reduced hatchling production of this nest. In the translocated nest, the mortality observed may have been caused by temperature variation between the original and the artificial nest due to weather degradation during artificial nest excavation. The translocation process took longer than expected (ca. 1hr), as the beach is located 30 minutes drive from Kelonia) and also because of the extra care taken during eggs removal and transport. Sand temperature is essential for the embryonic development of sea turtles eggs, not only for the embryo survival but also for the sex ratio (Mrosovsky 1982). Egg translocation has been shown to be effective in conservation of different sea turtles species (Dutton et al. 2005; Kornaraki et al. 2006) but it is a tool that should be used with a great care because of the possible impact on sex ratio output that can influence long-term population dynamics (Mrosovsky & Yntema 1980). In this particular case, the precautions taken during translocation allowed saving one of the rare nests laid in Réunion Island. In terms of sex ratio, we did not measure nest temperatures, but the information on incubation duration may be informative, given the relationship between incubation duration and sex ratio in green turtle nests (Godley et al. 2002). From the data on incubation duration (Table 1), there is a high probability that the translocated nest laid in January 2007 produced more females than the five other nests laid during a cooler period between June and August 2007.

ABELLA, E., A. MARCO, & L.F. LOPEZ-JURADO. 2007. Success of delayed translocation of loggerhead turtle nests. Journal of Wildlife Management 71: 2290-2296.

ACKERMAN, R. 1997. The nest environment and the embryonic develop¬ment of sea turtles. In: Lutz, P. & J. Musick (Eds) The Biology of Sea Turtles. Vol I. CRC Press, Boca Raton. pp. 83-106.

CICCIONE, S. & J. BOURJEA. 2006. Nesting of green turtles in Saint Leu, Réunion Island. Marine Turtle Newsletter 112:1-3.

DUTTON, D.L., P.H DUTTON, M. CHALOUPKA & R.H. BOULON. 2005. Increase of a Caribbean leatherback turtle Dermochelys coriacea nesting population linked to long-term nest protection. Biological Con¬servation 126: 186-194.

GODLEY, B.J., A.C. BRODERICK, F. GLEN & G.C. HAYS. 2002. Tem¬perature-dependent sex determination of Ascension Island green turtles. Marine Ecology Progress Series 226: 115-124.

KORNARAKI, E., D.A. MATOSSIAN, A.D. MAZARIS, Y.G MATSINOS & D. MARGARITOULIS. 2006. Effectiveness of different conservation measures for loggerhead sea turtle (Caretta caretta) nests at Zakynthos Island, Greece. Biological Conservation 130: 324-330.

LIMPUS, C.J., V. BAKER & J.D. MILLER, 1979. Movement induced mortality of loggerhead eggs. Herpetologica 35: 335-338.

LOUGNON, A. 1992 Sous le signe de la tortue. Voyages anciens à l’île Bourbon (1661-1725). Lib. Gérard Saint Denis.

MILLER, J. 1999. Determining clutch size and hatching success. In: K.L. Eckert, K.A. Bjorndal, F.A Abreu-Grobois & M. Donnelly (Eds.) Re¬search and Management Techniques for the Conservation of Sea Turtles. IUCN/MTSG Publication No. 4. pp. 124-129.

MROSOVSKY N. & C.L. YNTEMA. 1980. Temperature dependence of sexual differentiation in sea-turtles: implications for conservation prac¬tices. Biological Conservation 18: 271-280.

MROSOVSKY, N. 1982. Sex ratio bias in hatchling sea turtles from artifi¬cially incubated eggs. Biological Conservation 23: 309-314.